Blow moulding method

ABSTRACT

The disclosure relates to a method and apparatus for blow moulding hollow plastic articles each having at an end thereof, a main opening and a secondary opening defined by an angled passageway. The method includes the step of laterally stretching a tubular parison from which the article is to be moulded so as to receive a primary mandrel for forming said opening and a secondary mandrel for forming the passageway. Air is introduced into the parison through the secondary mandrel to form the inner end portion of the passageway while the parison is expanded to conform to the shape of the mould.

This invention relates generally to the art of blow moulding hollowarticles of plastic material, and is concerned in particular with animproved blow moulding method and apparatus.

Blow moulding is a well-known technique used for manufacturing hollowplastic articles such as bottles. Typically, a tube or "parison" ofplastic material in a hot, mouldable condition is positioned between twohalves or a partible mould having a mould cavity of a shape appropriateto the required external shape of the article to be moulded. The mouldhalves are closed around the parison and pressurized air is introducedinto the interior of the parison to cause it to expand and conform tothe shape of the mould cavity. The mould cools the plastic material toits final rigid shape and the mould is then opened and the articleremoved. The parison is normally extruded through a die directly intoposition between the mould halves; in this case, the overall process isreferred to as extrusion blow moulding.

Articles such as bottles having relatively wide cylindrical bodyportions and narrower necks can be blow moulded relatively easily.However, difficulties are often encountered in blow moulding articleshaving somewhat more unusual shapes. For example, it is difficult tosuccessfully blow mould an article which has a relatively large diameterneck and a body portion of corrugated or other unusual shape; the bodyportion may be of bellows-like form so as to allow for longitudinalextensibility and compressibility of the article. An example of anarticle of this type is a protective bellows or "boot" for an automotiverack and pinion steering system. In order to successfully mould thecorrugations defining the bellows-like portion of an article of thistype, a relatively small diameter parison must be used. If the parisonhas too large a diameter, "webs" will be formed between the corrugationsand the extensibility and compressibility of the bellows-like portion ofthe article will be lost. On the other hand, with a relatively smalldiameter parison it is difficult to successfully form the neck portionof the article.

The following references disclose various prior proposals formechanically expanding part of a parison in order to facilitate mouldingof articles having unusual shapes:

    ______________________________________                                        U.S. Pat. Nos.:                                                               1,514,183 (Steele et al)                                                                            3,311,950 (Strauss)                                     2,657,431 (Slaughter) 3,371,376 (Fischer)                                     3,009,196 (Hagen)     3,430,290 (Kinslow)                                     3,080,614 (Adams)     3,733,384 (Gerlovich)                                   3,164,646 (Fischer)   3,911,071 (Naumann)                                     3,278,665 (Harrison)  4,032 278 (Kuenzig)                                     3,303,249 (Strauss)   4,092,392 (Dunbeker)                                                          4,176,153 (Weiler et al)                                French Patents Nos.:                                                          1,373,990 (Lackner)                                                           1,495,618 (Mehnert)                                                           1,175,974 (Ateliers et Forges de la Loire)                                    1,415,747 (AGK)                                                               1,441,298 (B.A.S.F.)                                                          British Patent No.:                                                             781,560 (Glenn Proprietary)                                                 German Offenlegungsschriften:                                                 1,479,216 (Fischer)                                                           1,604,632 (Moslo)                                                             German Auslegeschrift:                                                        1,178,580 (Hagen)                                                             ______________________________________                                    

Another problem encountered in manufacturing articles such as vehiclesteering boots is occasioned by the fact that the interior of the bootmust be vented when the boot is to be used for a steering system whichis power assisted. Such a system will normally have one boot at eachside and the boot will be interconnected by a vent tube so that airdisplaced from one boot as it is compressed when the system is operatedis displaced along the vent tube and into the other boot, which will beexpanding at this time. This requires that each boot be provided with anintegral port or nipple into which an end portion of the vent tube canbe fitted. Typically, the nipple is required to take the form of a smalltubular extension which projects outwardly from the boot adjacent itslarge diameter neck and which has an outer end portion closely adjacentto but spaced from the neck and extending about an axis parallel to thelongitudinal axis of the boot. The passageway through the nipple mustobviously communicate with the interior of the boot for venting, whichmeans that the passageway must be angled at its inner end. In otherwords, the nipple has a passageway comprising an outer end portionparallel to the longitudinal axis of the bellows as a whole, and aninner end portion which is angled inwardly and which communicates withthe interior of the bellows.

Manufacture of a boot having an integral nipple of this form presentssignificant practical difficulties. Attempts have been made to injectionmould the nipples separately from the remainder of the article and thenattach the nipple by heat welding. However, this requires expensivewelding machinery and involves a separate manual operation. In practice,a high scrap rate was encountered in manufacturing boots by this method.

An object of the present invention is to provide an improved blowmoulding method by which nipples and like formations may be integrallyformed as part of such an article. In one aspect, the method andapparatus of the invention is intended to permit the blow moulding ofany plastic article having a hollow body portion which defines aninternal space, a main opening at an end of said portion communicatingwith said space and extending about a first axis, and a passagewaydefining a secondary opening adjacent said main opening, said passagewayincluding an outer portion which extends about a second axis spaced fromand generally parallel to said first axis, and an inner portion which isinclined inwardly towards said axis and communicates with said internalspace.

One aspect of the method of the invention includes a first step ofproviding a partible mould comprising mould parts which can be openedand closed and which, when closed, define a mould cavity of a shapeappropriate to the required external shape of the article and extendingabout a longitudinal axis corresponding to said first axis of thearticle. With the mould parts open, a tubular parison of thermoplasticmaterial in a mouldable condition is positioned between the partsgenerally on said longitudinal axis. The parison includes an end portionat which the main and secondary openings of the article are to be formedand the parison has a radial dimension less than the spacing between thefirst and second axes of the article. A primary mandrel and a secondarymandrel are provided and are shaped to form respectively said mainopening and the outer portion of the passageway in the article to bemoulded. The mandrels are disposed respectively on the longitudinal axisand on a secondary axis corresponding to said second axis of thearticle. The secondary mandrel has an air duct which includes an airoutlet disposed at an outer end of the mandrel and which is arranged sothat air leaving the outlet in use will form said inner end portion ofthe passageway in the article. The end portion of the parison isstretched laterally to an extent sufficient to permit the mandrels toenter said end portion. The mandrels are then moved respectively alongsaid longitudinal and secondary axes into the end portion of theparison. The mould parts are closed about the mandrels and the end ofthe parison opposite said one end is closed. The next step is tointroduce air into the interior of the parison to cause the parison toexpand and adopt the shape of the mould cavity. This step includescausing air to flow into the parison by way of the air duct in thesecondary mandrel whereby the inner end portion of the passageway in thearticle is formed by air flowing from said air duct into the internalspace of the body portion of the article. The parison is allowed to coolat least to a semi-rigid state in which it can be handled and the mouldparts are opened to permit removal of the moulded article.

In order that the invention may be more clearly understood, referencewill now be made to the accompanying drawings which illustrate apreferred embodiment of the invention by way of example, and in which:

FIG. 1 is a perspective view of a "boot" for a power-assisted rack andpinion steering system, manufactured in accordance with the invention;

FIG. 2 is a side elevation, partly in section, of a moulding apparatusaccording to the invention with the mould parts shown in the openposition;

FIG. 3 is a somewhat diagrammatic partial vertical sectional viewgenerally on line III--III of FIG. 2, the section being taken in a planegenerally normal to the plane of FIG. 2;

FIG. 4 is a plan view of the stretcher mechanism used for expanding theparison in accordance with the method of the invention; and,

FIG. 5 is an inverted plan view with surrounding structure omitted oftwo mould inserts which are visible in section in FIGS. 2 and 3.

Reference will first be made to FIG. 1 in briefly describing a steeringboot as a typical example of a plastic article which may be blow mouldedin a single operation in accordance with the method and apparatusprovided by the invention. The boot is generally denoted by referencenumeral 10 and includes a hollow body portion 12 of corrugated or"bellows" form. The body portion has an internal space and extends abouta first axis denoted "X--X". A main opening 14 is provided at one end ofthe body portion and extends about axis X--X in communication with theinternal space of the body portion. Opening 14 is defined by arelatively wide neck 12a at the relevant end of the body portion 12. Acorresponding but much smaller neck 12b is provided at the opposite endof the body portion and defines a smaller opening at other end of theboot.

Formed externally on body portion 12 is an integral nipple 16 which hasan internal passageway communicating with the internal space of the bodyportion and defining a secondary opening 18 adjacent the main opening14. The internal passageway of nipple 16 has an outer portion 16a whichextends about a second axis Y--Y spaced from and generally parallel tothe first axis X--X. The passageway also has an inner end portion 16bwhich is inclined inwardly towards axis X--X and which communicates withthe internal space of the body portion.

As has been explained previously, there are two primary problemsassociated with the manufacture of boot 10 is a single blow mouldingoperation. Firstly, a relatively small diameter parison must be used inorder to successfully mould the corrugations in the body portion of thearticle, but using such a parison, it is difficult to successfully formand size the relatively wide neck 12a required in this type of article.The second problem is to integrally form nipple 16 with the remainder ofthe article.

Referring now to FIGS. 2 and 3, the blow moulding apparatus used to makeboot 10 includes a partible mould comprising first and second mouldparts denoted 20 and 22 respectively. In this particular embodiment,each part forms one half of the mould and the mould halves are movablebetween the open position in which they are shown in FIG. 2 and a closedposition. For clarity of illustration, the drawings do not show supportsfor the mould halves or the means employed to move them between the openand closed positions. These components are entirely conventional andwill be well known to persons skilled in the blow moulding art.

The mould parts are machined to define specially shaped recesses 20a and22a respectively which co-operate when the mould is closed to define amould cavity which extends about a longitudinal axis; this axiscorresponds with the first axis X--X of the article and is thereforesimilarly designated. The mould cavity is of a shape appropriate to therequired external shape of the article to be moulded, in this case theboot 10. Part of the article is visible in longitudinal section at 10 inFIG. 3. The mould parts also include movable mould inserts 38 and 40which are more particularly illustrated in FIG. 5 and which will bedescribed later in connection with that view.

Referring back to FIG. 2, the boot 10 is moulded from a tubular parison42 of a thermoplastic material. The parison is shown in the position itoccupies immediately before the mould halves 20 and 22 are closed priorto commencement of the actual blow moulding operation. At this time, theparison will be in a mouldable condition; that is, the plastic materialof which the parison is made will be hot and in a form in which it canbe relatively easily deformed by the application of internal airpressure. Normally, the parison will in fact be formed by a sectionsevered transversely from a tubular extrusion fed continuously orintermittently to the moulding apparatus from an extruder as isconventional in the blow moulding art. In FIG. 1, the parison is shownsupported from the extruder.

For the reasons discussed above, parison 42 is of relatively smalldiameter and in fact has a radial dimension less than the spacingbetween the axes X--X and Y--Y of the moulded article. The apparatustherefore includes a "stretcher mechanism" for mechanically engaging andexpanding the lower end portion of the parison. The mechanism isgenerally indicated by the reference numeral 44 and will be described indetail later.

Before referring to the stretcher mechanism, however, it will beconvenient to identify a mandrel assembly which appears in the center ofthe stretcher mechanism as seen in FIGS. 2 and 3. The mandrel assemblyincludes a primary mandrel 46 and a secondary mandrel 48. The secondarymandrel appears in front of the primary mandrel in FIG. 2 and the twomandrels can best been seen in FIG. 3. The main mandrel is of relativelylarge diameter and is designed to define the shape of and accuratelysize the neck 12a of the article. Mandrel 46 extends about thelongitudinal axis X--X of the apparatus. Mandrel 48 is of relativelysmall diameter and is shaped to form the outer portion 16a of thepassageway in the nipple 18 of the moulded article (see FIG. 1). Mandrel48 has an internal air duct 50 which includes an air outlet 50a at theouter end of the mandrel arranged so that air leaving the outlet will bedirected inwardly towards axis X--X and form the inner end portion 16bof the passageway in nipple 16. In other words, the air issuing fromoutlet 50a will blow through the plastic material which might otherwisetend to obstruct the inner end portion of the passageway so that thepassageway is properly formed and will be clear internally.

Air is also introduced into the interior of the parison through a blowpin 51 which extends upwardly from the top of the main mandrel 46. Blowpin 51 is of conventional form and communicates with an air duct (notshown) in mandrel 46. The two air ducts in the respective mandrels aresupplied with air from a suitable compressed air supply as isconventional in the art. Blow pin 51 is also visible in FIG. 2 and has aseries of openings in its external surface through which air issues intothe interior of the parison to expand the same. In that view, themandrels 46 and 48 are shown in retracted positions such as they wouldoccupy just after the parison 42 had been formed but before the mouldparts have been closed and blowing has taken place. In FIG. 3, on theother hand, the mandrels are shown in their elevated positions as duringblow moulding. The retracted positions of the upper ends of therespective mandrels are shown in ghost outline. The mechanism for movingthe mandrels between their advanced and retracted positions will bedescribed later.

Referring particularly to FIGS. 2 and 4, stretcher mechanism 44 includesa plurality of parison engaging "fingers" arranged in an annular seriesaround the mandrel blow pin 51 adjacent the lower end of the mouldparts. Two of these fingers are visible at 52 in FIG. 2; however, byreference to FIG. 4, will be seen that eight such fingers are in factprovided and are spaced equally about the blow pin. Each finger projectsupwardly from a horizontally movable slide 54 parallel to thelongitudinal axis of mould cavity 24. The slides 54 are movablesimultaneously to move the fingers between the normal rest positions inwhich two of the fingers are shown in FIG. 2, in which the fingers areall disposed closely adjacent to the blow pin 51 (and within the lowerend of the parison 42) and retracted positions as shown in FIG. 4, inwhich the fingers have been moved outwardly to expand the lower endportion of the parison generally to the shape indicated at 42' in FIG.4.

It will be noted that the fingers 52 move radially with respect to themould cavity axis X--X at all times. However, the fingers 52 do not allmove to the same radial extent. The primary and secondary mandrels arevisible in FIG. 4 at 46 and 48 respectively and it will be noted thatthe finger closest to the secondary mandrel 48 (denoted 52') has movedradially further away from axis X--X and the other fingers and that thefingers on either side of finger 52' (denoted 52") has moved anintermediate distance so that the parison has been laterally stretchedat the position of the secondary mandrel to an extent sufficient topermit that mandrel to enter the end portion of the parison when themandrel is raised. This lateral stretching of the parison is not ofcourse visible in FIG. 2 because the sectional view represented by FIG.2 is taken in a plane normal to the plane on which the mould parts meet(denoted P in FIG. 4) and the parison is expanded symmetrically in thatplane.

This differential movement between different ones of the fingers 52 isalso illustrated in FIG. 3 in which finger 52' is shown in full lines inits retracted (parison expanding) position and in chain-dotted outlinein its advanced position; the diametrically opposite finger 52 issimilarly illustrated and it can be seen that finger will move over amuch smaller radial distance than finger 52'. This differential movementis achieved by providing differently shaped cam tracks for controllingmovement of the slides on which the fingers are mounted as will bedescribed below.

Movement of the fingers between their rest positions and retracted(parison expanding) positions is controlled by a pneumatic cylinder andram device generally denoted 56 and shown in FIG. 4 only. The slides 54which carry the fingers 52 are mounted in respective radial grooves orslideways 60 in the underside of a cover plate 62 secured by bolts 64 toa housing 58 (see also FIG. 2). As seen in FIG. 4, the slides aresubstantially in their fully retracted positions.

Below the slides, housing 58 is shaped to define an annular recess 66(FIG. 2) which receives an annular member 68 forming an actuator ringfor the fingers 52. Ring 68 is mounted for free turning movement inrecess 66 by way of ballbearings 70. Each of the slides 54 is fittedwith a pin 72 which depends from the slide and is received in an arcuategroove 74 (FIG. 4) in the upper face of ring 68. A bearing sleeve 76 isfitted around the lower portion of each pin 72 within groove 74. Similargroove and pin arrangements are provided for each of the slides 54. Thegrooves 74 in effect define cam tracks and are specially shaped so thatangular movement of ring 68 causes all of the slides 54 to move radiallyin or out depending on the direction in which the ring is turned. Forexample, if ring 68 is turned in the counter-clockwise direction as seenin FIG. 4, the cam tracks 74 will all act on the associated bearingsleeves 76 and pins 72 to cause all slides 54 and associated fingers 52to move inwardly towards the blow pin 58. Conversely, if the fingers 52are in the rest (advanced) positions adjacent blow pin 51 and ring 68 isturned in the clockwise direction, the fingers will all simultaneouslymove outwards. The extent of this movement in either case is determinedby the length of the cam tracks 74 and the angular extent through whichring 68 is turned.

The cam track for the slide associated with finger 52' is denoted 74'and is somewhat steeper (less arcuate) than the cam tracks associatedwith the other fingers so that finger 52' will move radially furtheroutwards than the other fingers. Similarly, the cam tracks associatedwith the fingers 52" are denoted 74" and are curved slightly more thantrack 74' but less than the other cam tracks. This differential incurvature between the various tracks makes for correspondingdifferentials in the radial movement of the associated fingers.

Angular movement of the ring 68 is effected by the cylinder and ramdevice 56 referred to above. The ram of device 56 is indicated at 78 andhas a coupling 80 at its outer end. A link pin 82 extends verticallyupwardly from coupling 80 through an arcuate slot 84 in the bottom wallof housing 58 and is secured to ring 68 at its upper end. Thus, as ram78 is extended and retracted, ring 68 will move through discreet angularamounts. The amount of this angular movement will be determined by thestroke of ram 78, which will be selected as appropriate to the requiredmovement of the fingers 52.

In an alternative embodiment, cylinder and ram device 56 may be replacedby a hydraulic motor arranged with its drive shaft vertical and fittedat its upper end with a spur gear which meshes with a corresponding ringgear fitted to the underside of ring 68 so that the ring can be turnedby operating the motor. Obviously, the motor would have to be suitablygeared and would be reversible.

FIG. 2 illustrates how the slides 54 which support the fingers 52 alsoserve to define the position of the parison 52 prior to commencement ofthe blow moulding operation. Thus, the parison should be disposed sothat a lower end portion thereof extends beyond the lower ends of themould parts 20 and 22. In the described illustrated embodiment, this endportion of the parison is engaged by the fingers 52 of the stretchermechanism 44 and is expanded. However, in an alternative embodiment ofthe invention, the fingers could engage the parison within the range ofmovement of the mould parts, in which case the stretcher mechanism wouldbe designed to be retracted downwardly when the mould parts are closed.In any event, the parison should preferably not be expanded beyond itsrequired final size and shape since otherwise there may be a tendencyfor the parison to become trapped or crimped when the mould parts close.

As discussed previously, expansion and stretching of the lower endportion of the parison by the fingers 52 allows the mandrels 56 and 58to move upwardly into the parison. This movement is effected by apneumatic cylinder and ram device 86 (FIG. 2) which is mounted in avertical position below the mandrel assembly and the ram of which iscoupled to said assembly. Thus, the ram is fitted with a transverseplate 88 on which the main mandrel 46 is mounted. A bracket 90 isclamped around mandrel 46 at a position spaced above plate 88 andmandrel 48 is secured to this bracket by a bolt 92 which extendsupwardly through a part of the bracket and which is screw-threaded intothe lower end of the mandrel. Bolt 92 is formed as a coupling for theair supply to mandrel 48. Blow pin 51 extends upwardly from the top ofmandrel 46 as mentioned previously and only part of the pin is visiblein FIG. 3. The upper end of the blow pin (see FIG. 2) is shaped toco-operate with the mould parts and close the upper end of the parisonwhen the mandrels are in their raised positions.

At this time, only upper end portions of the two mandrels actually enterthe parison. These portions co-operate with the mould inserts 38 and 40referred to previously and both the mandrels and the inserts are closelydimensioned so that the neck area of the moulded article and the nipple16 are formed by compression between the inserts and the mandrels ratherthan by blow moulding as such. In other words, the neck area of thearticle is in fact compression moulded while the body portion is blown(as is the inner end portion of the passageway in nipple 16).

An annular groove 94 is provided around the upper end portion of mandrel46 so as to form a corresponding protuberant rib inside the neck of themoulded article. Similar grooves 96 are provided around the upper endportion of mandrel 48 for forming similar ribs inside nipple 16. Theseribs assist in properly securing the boot to the steering systemcomponents when the article installed. The mould inserts 38 and 40 aredesigned to be retractable away from the mandrels to free the neck ofthe moulded article and allow it to flex sufficiently to permit themandrel to be withdrawn without damaging the moulded ribs formed by thegrooves 94 and 96. The mould parts 20 and 22 are provided withrespective parallel sided recesses which receive the inserts and allowthem to slide towards and away from one another from their normalmoulding positions to retracted positions in which pressure on themoulded article is relieved. Insert 38 is visible in FIG. 3 and it willbe seen that the insert is formed with projecting flanges 38d which arereceived in a complementary undercut portion of the recess in mould half20 so as to permit this sliding movement of the insert. Insert 40 issimilarly supported in mould half 22. The inserts have respectiveinwardly projecting peripheral edges as edge 38b (FIG. 3) at their lowerends which co-operate with mandrels to cut off the surplus lower endportion of the parison when the mould halves are closed.

Movement of the two inserts between their advanced and retractedpositions is effected under the control of respective pneumatic cylinderand ram devices 112 and 114 which are horizontally mounted behind themould parts and portions of which are visible in FIG. 2. With continuedreference to that view, it will be seen that the inserts 38 and 40 areshaped at their outer sides to define respective undercut slideways 116and 118 which slidably interlock with associated actuator slides. Theseactuator slides are coupled to the respective cylinder and ram devices112 and 114. The slides have not been shown in detail but, the twoinserts 38 and 40 are shown in plan in FIG. 5; it is sufficient to notethat the slides are generally wedge shaped and that the slideways 116and 118 on the inserts are inclined with respect to the joint linebetween the two mould halves 20 and 22. Thus, longitudinal movement ofthe respective slides under the control of their associated cylinder andram devices 112 and 114 will cause corresponding radial movement of theinserts 38 and 40 with respect to the mould cavity 24.

Referring now to FIG. 5, it will be seen that each of the inserts 38 and40 has a main arcuate shaped recess for receiving the main mandrel and asmaller similarly shaped recess in which the secondary mandrel isreceived. The respective recesses in insert 38 are denoted 38a and 38bwhile the corresponding recesses in insert 40 are denoted 40a and 40b.Insert 40 is provided with a slide 120 which is biassed towards recess40b by a compression spring 122. Slide 120 has an outer edge 120a curvedto engage mandrel 48 inwardly of recess 40b and is retained by a pin 124which extends through a longitudinal slot in the slide so that, when theinserts are apart, the slide can move within the limits allowed by theslot. Slide 120 is generally T-shaped cross-section and is received in aT-shaped slideway 125, the cross-sectional shape of which can be seen inFIG. 3. A similar spring biassed slide, generally denoted 120', isprovided in insert 38. The purpose of the spring-biassed slides is toapply a slight retaining force against the nipple on the moulded articleas mandrel 48 is withdrawn so as to minimize the risk of distorting thenipple.

The apparatus provided by the invention is supported by four supportcolumns, two of which are visible at 128 in FIG. 2, and which extendupwardly from a base plate 130; the columns are provided with screwadjusters 132 at their lower ends. At their upper ends, the four supportcolumns are attached to the actuator housing 58 by four bolts 134 (FIG.4). The device 86 for actuating the mandrel assembly is carried bybrackets 136 depending from housing 58.

A typical moulding sequence will now be described primarily withreference to FIGS. 2 and 3.

With the mould halves 20 and 22 in their open positions and mandrelassembly retracted, the parison 42 is positioned over the exposedportion of the mandrel blow pin 51. Typically, the parison will beextruded into this position and supported at its upper end by theextrusion device. At this time, the cylinder and ram devices 112 and 114associated with the mould inserts 38 and 40 will be actuated so that theinserts will be in their forward (moulding) positions and the fingers 52will be in their normal rest positions adjacent blow pin 51. After theparison has reached the position shown in FIG. 2, the fingers 52 will bemoved outwardly by actuating cylinder and ram device 56 to expand andstretch the lower end portion of the parison. Next, the mandrels 46 and48 will move up into the position in which they are shown in FIG. 3inside the parison. The mould halves then close onto the mandrels,trapping the parison.

Air pressure is now introduced into the parison through the mandrel blowpin 51 and through mandrel 48. This expands the parison into contactwith the mould halves and causes it to conform to the shape of the mouldcavity. At the same time, the inner end portion 16b of the passageway innipple 16 is formed. The parison then cools into a relatively rigidstate. Air pressure is then released and the rams of the cylinder andram devices 112 and 114 are retracted to retract the mould inserts 38and 40 and relieve external pressure on the neck of the moulded article.

Next, the mandrels are retracted and the mould halves open leaving themoulded article supported by the fingers 52 and slides 54. Finally, themoulded article is removed easily manually or by an air cylinderactuated "wiper" mechanism in manner known per se. The inserts 38 and 40are then returned to their forward positions ready for the nextoperation.

It will of course be appreciated that the preceding description relatesto a preferred embodiment of the invention only and that manymodifications are possible within the broad scope of the invention.Also, it is to be noted that the method and apparatus disclosed hereinmay be used for moulding articles other than the article specificallyreferred to above. According to another aspect, the method and apparatusof the invention may be used to manufacture an article in which thesecondary opening is not disposed about an axis parallel to the axis ofthe main opening of the article; in other words, referring to FIG. 1 ofthe drawings, axis Y--Y need not be parallel to axis X--X. For example,nipple 16 could extend about an axis disposed at an angle to axis X--X(e.g. a 45° angle). In that event, the secondary mandrel would have tobe provided with a separate actuating device; in other words, the twomandrels could not be actuated by the same cylinder and ram device inthe manner shown in the drawings. There is no limitation to articles ofcircular cross-section although special arrangements will obviously haveto be provided for stretching the parison where the article is to be ofnon-circular shape.

The movable inserts 38 and 40 although desirable in the presentinstance, are not essential. For example, there would be no need forsuch inserts if the neck of the moulded article were plain.

Also, it may not be necessary to radially expand the inner end portionof the parison in all cases. Depending on the article, in some cases, itmight be sufficient to merely stretch the parison to receive thesecondary mandrel. The fingers around the remainder of the parison wouldthen remain stationary and simply hold the parison in place or thosefingers might even be omitted in some cases.

I claim:
 1. A method of blow moulding a plastic article having a hollowbody portion which defines an internal space, a main opening at an endof said portion communicating with said space and extending about afirst axis, and a passageway defining a secondary opening adjacent saidmain opening, said passageway including an outer portion which extendsabout a second axis spaced from and generally parallel to said firstaxis, and an inner portion which is inclined inwardly towards said firstaxis and communicates with said internal space,the method comprising thesteps of: providing a partible mould comprising mould parts which can beopened and closed and which, when closed, define a mould cavity of ashape appropriate to the required external shape of the article andextending about a longitudinal axis corresponding to said first axis ofthe article; with said mould parts open, positioning between said partsgenerally on said longitudinal axis, a tubular parison of athermoplastic material in a mouldable condition, said parison includingan end portion at which said main and secondary openings of the articleare to be formed and having a radial dimension less than the spacingbetween said first and second axes of the article; providing a primarymandrel and a secondary mandrel shaped to form respectively said mainopening and the outer portion of said passageway in the article to bemoulded, said mandrels being disposed respectively on said longitudinalaxis and a secondary axis corresponding to said second axis of thearticle, and said secondary mandrel having an air duct which includes anair outlet disposed at an outer end of the mandrel and arranged so thatair leaving said outlet in use will form said inner end portion of thepassageway; laterally stretching said end portion of the parison to anextent sufficient to permit said mandrels to enter said portion, by bothradially expanding said end portion and laterally distorting saidportion at the position of said secondary axis along which the secondarymandrel is movable; moving said mandrels respectively along saidlongitudinal axis and said secondary axis into said end portion of theparison; closing the mould parts about said mandrels and closing the endof the parison opposite said one end; introducing air into the interiorof the parison to cause the parison to expand and adopt the shape of themould cavity, including causing air to flow into the parison by way ofsaid air duct in the secondary mandrel, whereby said inner end portionof the passageway is formed by air flowing from said duct into theinternal space in the body portion of the article; allowing the parisonto cool at least to a semi-rigid state in which it can be handled; and,opening the mould parts to permit removal of the moulded article.
 2. Amethod as claimed in claim 1, wherein said step of laterally stretchingthe end portion of the parison is performed by providing a plurality ofparison-engaging elements which are arranged in a generally annularconfiguration about said longitudinal axis of the mould cavity and whichprojects into said end portion of the parison generally parallel to saidaxis, and simultaneously moving all of said elements radially outwardlywith respect to said axis along rectilinear paths which extend normal tosaid axis while maintaining the elements generally parallel to said axisand leaving said end of the parison unobstructed, at least one of saidelements at the position of said secondary axis being moved through aradial distance greater than the remainder of said elements so as tocause said lateral distortion of the shape of the parison.
 3. A methodas claimed in claim 1, wherein said mould parts include respectiveinserts defining surface portions of said mould cavity for defining theexternal shape of the article in the region of said main opening andpassageway, and wherein each said mandrel defines at least one externalannular groove for forming an inwardly protuberant rib in the respectiveopening in the moulded article, and where the method comprises thefurther steps of:withdrawing said mandrels from the parison after theparison has been expanded by air pressure; and, relieving the pressurebetween said inserts and the mandrels after the parison has beenexpanded but before withdrawing the mandrels, to permit the mouldedarticle to flex and allow disengagement of the moulded ribs from saidgrooves in the mandrels as the mandrels are withdrawn.
 4. A method asclaimed in claim 3, comprising the further step of mechanicallyrestraining the portion of the moulded article in which said passagewayis formed as the secondary mandrel is withdrawn.
 5. A method of blowmoulding a plastic article having a hollow body portion which defines aninternal space, a main opening at an end of said portion communicatingwith said space and extending about an axis, and a secondary openingdisposed adjacent said main opening, and communicating with saidinternal space,the method comprising the steps of: providing a partiblemould comprising mould parts which can be opened and closed and which,when closed, define a mould cavity of a shape appropriate to therequired external shape of the article and extending about alongitudinal axis corresponding to said axis of the article; with saidmould parts open, positioning between said parts generally on saidlongitudinal axis, a relatively narrow tubular parison of athermoplastic material in a mouldable condition, said parison includingan end portion at which said main and secondary openings of the articleare to be formed; providing a primary mandrel and a secondary mandrelshaped to form respectively said main and secondary openings, saidsecondary mandrel having an air duct which includes an air outletdisposed at an outer end of the mandrel; laterally stretching said endportion of the parison to an extent sufficient to permit said mandrelsto enter said portion, by both radially expanding said end portion andlaterally distorting said portion at the position at which saidsecondary mandrel is to enter said portion; moving said mandrels intosaid end portion of the parison;closing the mould parts about saidmandrels and closing the end of the parison opposite said one end;introducing air into the interior of the parison to cause the parison toexpand and adopt the shape of the mould cavity, including causing air toflow into the parison by way of said air duct in the secondary mandrel,whereby air flows from said duct into the internal space in the bodyportion of the article and ensures communication between said secondaryopening and said internal space; allowing the parison to cool at leastto a semi-rigid state in which it can be handled; and, opening the mouldparts to permit removal of the moulded article.